20,397 research outputs found
A new approach to axial coupling constants in the QCD sum rule
We derive new QCD sum rules for the axial coupling constants by considering
two-point correlation functions of the axial-vector currents in a one nucleon
state. The QCD sum rules tell us that the axial coupling constants are
expressed by nucleon matrix elements of quark and gluon operators which are
related to the sigma terms and the moments of parton distribution functions.
The results for the iso-vector axial coupling constants and the 8th component
of the SU(3) octet are in good agreement with experiment.Comment: 10 pages, 1 figure include
Realization of Strong Coupling Fixed Point in Multilevel Kondo Models
Impurity four- and six-level Kondo model, in which an ion is tunneling among
four- and six-stable points and interacting with surrounding conduction
electrons, are investigated by using the perturbative and numerical
renormalization group methods. It is shown that purely orbital Kondo effects
occur at low temperatures in these systems which are direct generalizations of
the Kondo effect in the so-called two-level system. This result offers a good
explanation for the enhanced and magnetically robust Sommerfeld coefficient
observed in SmOs_4Sb_12 and some other filled-skutterudites.Comment: 3 pages, 3 figures, for proceedings of ASR-WYP-2005. To be published
in Journal of Physical Society Japan supplemen
Renormalizing a BRST-invariant composite operator of mass dimension 2 in Yang-Mills theory
We discuss the renormalization of a BRST and anti-BRST invariant composite
operator of mass dimension 2 in Yang-Mills theory with the general BRST and
anti-BRST invariant gauge fixing term of the Lorentz type. The interest of this
study stems from a recent claim that the non-vanishing vacuum condensate of the
composite operator in question can be an origin of mass gap and quark
confinement in any manifestly covariant gauge, as proposed by one of the
authors. First, we obtain the renormalization group flow of the Yang-Mills
theory. Next, we show the multiplicative renormalizability of the composite
operator and that the BRST and anti-BRST invariance of the bare composite
operator is preserved under the renormalization. Third, we perform the operator
product expansion of the gluon and ghost propagators and obtain the Wilson
coefficient corresponding to the vacuum condensate of mass dimension 2.
Finally, we discuss the connection of this work with the previous works and
argue the physical implications of the obtained results.Comment: 49 pages, 35 eps-files, A number of typographic errors are corrected.
A paragraph is added in the beginning of section 5.3. Two equations (7.1) and
(7.2) are added. A version to be published in Phys. Rev.
Future of Ultraviolet Astronomy Based on Six Years of IUE Research
Physical insights into the various astronomical objects which were studied using the International Ultraviolet Explorer (IUE) satellite. Topics covered included galaxies, cool stars, hot stars, close binaries, variable stars, the interstellar medium, the solar system, and IUE follow-on missions
Optically nonlinear energy transfer in light-harvesting dendrimers
Dendrimeric polymers are the subject of intense research activity geared towards their implementation in nanodevice applications such as energy harvesting systems,organic light-emitting diodes, photosensitizers, low-threshold lasers, and quantum logic elements, etc. A recent development in this area has been the construction of dendrimers specifically designed to exhibit novel forms of optical nonlinearity, exploiting the unique properties of these materials at high levels of photon flux. Starting from a thorough treatment of the underlying theory based on the principles of molecular quantum electrodynamics, it is possible to identify and characterize several optically nonlinear mechanisms for directed energy transfer and energy pooling in multichromophore dendrimers. Such mechanisms fall into two classes: first, those where two-photon absorption by individual donors is followed by transfer of the net energy to an acceptor; second, those where the excitation of two electronically distinct but neighboring donor groups is followed by a collective migration of their energy to a suitable acceptor. Each transfer process is subject to minor dissipative losses. In this paper we describe in detail the balance of factors and the constraints that determines the favored mechanism, which include the excitation statistics, structure of the energy levels, laser coherence factors, chromophore selection rules and architecture, possibilities for the formation of delocalized excitons, spectral overlap, and the overall distribution of donors and acceptors. Furthermore, it transpires that quantum interference between different mechanisms can play an important role. Thus, as the relative importance of each mechanism determines the relevant nanophotonic characteristics, the results reported here afford the means for optimizing highly efficient light-harvesting dendrimer devices
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